Our 4' x 4' x 18" veggie filter is functionally a vortex with root
filters. The water comes in at a corner, parallel to the side...call
that south west corner, going north. It falls into the pond. The
exit is at the south east top corner going east. The celery roots
actually restrict the circular flow. It takes over 45 min to turn
over the volume. Almost all of the muck gets dropped before the
exit. It then goes through a 4' x 8' x 18" veggie filter with more
roots. Water enters there from the southwest, going east and exits at
the far top going east. The hyacinth roots clean out what remains of
the muck. Not pure vortex, but really effective. Little much gets to
the second pond, which takes 1.5 hours to turn over. Slow filtration
is a key element!

Jim